Comorbidities in severe asthma are common and contribute to disease burden. The severe asthma phenotype and treatment response can be impacted by comorbid conditions. Real-world data on the use of mepolizumab in severe eosinophilic asthma (SEA) in the presence of comorbidities are needed to inform clinical practice. To investigate the impact of comorbid conditions on baseline phenotype in patients with SEA and assess the mepolizumab treatment effect by comorbidity status in SEA. Patients enrolled in the Australian Mepolizumab Registry (n = 309) were classified into subgroups defined by the presence or absence of comorbidities, including nasal polyps, aspirin-exacerbated airway disease, asthma-chronic obstructive pulmonary disease overlap (ACO), fungal sensitization, and obesity. Patient baseline characteristics were compared, and the impacts of comorbidity on phenotype, identified by differences in patient age and/or baseline biomarker levels and/or asthma severity, were assessed. The mepolizumab treatment effects on clinical and biological outcomes at 12 months were assessed. Across comorbidity subgroups, mepolizumab reduced the rate of clinically significant exacerbations (range: 47%-77%), maintenance oral corticosteroid use (dose reduction: 4.2-13.3 mg/d), and improved symptom control (Asthma Control Questionnaire-5 score: 1.9-2.4 point reduction) and lung function (mean: 3.4-9.3 post-bronchodilator percent predicted forced expiratory volume in 1 second). Peripheral blood eosinophils were reduced (mean: 480-780 cells/μL). Comorbidities (nasal polyps, obesity, ACO, and fungal sensitization) modified the baseline phenotype. Mepolizumab treatment is associated with comparable clinical improvements in patients with SEA and comorbidities. Mepolizumab effectively minimizes the disease impact and corticosteroid burden in patients with SEA.